This invention relates to the technology of an illuminating device and a liquid-crystal display apparatus, more particularly, to an illuminating device for use in a liquid-crystal display apparatus that is capable of producing high-contrast image over a wide range of viewing angles, as well as a liquid-crystal display apparatus that makes use of the illuminating device.
The use of liquid-crystal displays (LCDs) as a display for word processors and computers is rapidly increasing today. The use of LCDs as a monitor in ultrasonic, CT and MRI diagnostic apparatus is under review. Conventionally, these medical diagnostic apparatus have primarily used CRTs (cathode-ray tubes) as a monitor.
LCDs have many advantages such as ease in size reduction, small thickness and lightweightness. On the other hand, they have poor viewing angle characteristics (narrow viewing angle) since as the viewing direction or angle changes, the contrast of an image decreases sharply and the gradation also reverses to have the image look differently. As a result, depending on the position of the viewer, the image cannot be viewed correctly.
In the medical applications described above, correct viewing of images is important particularly for preventing wrong diagnosis. What is more, diagnosis based on the difference in image density requires that images of high contrast ratio be displayed over a wide range of viewing angles. Another problem peculiar to medical monitors is that image is usually displayed in monochrome (black and white colors) and, hence, suffers considerable drop in contrast as the viewing angle varies.
A known method for increasing the viewing angle of LCDs relies upon using collimated backlight and the image-bearing light that has passed through the liquid-crystal display panel is diffused with a diffusing plate. This method increases the viewing angle of the liquid-crystal display and enables the fabrication of an LCD that produces high-contrast image display over a wide range of viewing angles.
This method has the advantage that the higher the directivity of collimated light, the wider the viewing angle that can be offered. On the other hand, if the performance of the optical collimator used is so low that collimated light having adequate directivity cannot be launched into the liquid-crystal display panel, the desired viewing angle cannot be produced.
In addition, uneven display and blurred images often occur if the directivity of collimated light is low. Since incorrect recognition of an image can cause wrong diagnosis or inconsistency in the results -of diagnosis, the uneven display and blurred images are particularly serious problems in the medical applications.
The present invention has been accomplished under these circumstances and has as a primary object providing an illuminating device that can emit collimated light of very high directivity and which, if combined with a light diffusing plate in a liquid-crystal display apparatus, can produce a wide range of viewing angles and which yet can display high-quality images without unevenness and blur that would otherwise result if a collimator of low performance were used to produce collimated light of low directivity.
Another object of the invention is to provide a liquid-crystal display apparatus that makes use of the illuminating device and can display high-quality images free from unevenness and blurring with high contrast over a wide range of viewing angles.
In order to attain the primary object described above, the present invention provides an illuminating device comprising light sources, a housing of the light sources that has its inner surfaces-covered with a diffuse reflecting layer, an optical collimator for collimating light issued from the light sources and the light reflected by the diffuse reflecting layer, and a directivity regulating member for regulating directivity of the collimated light emerging from the optical collimator.
Preferable, the directivity regulating member has a plurality of optical paths through which the light passes and anti-reflection layers that absorb the light incident on wall surfaces of the optical paths.
Preferably the following relation is satisfied:
p/tan xcex8xe2x89xa6La
where p is a pitch of emergence of the collimated light from the optical collimator, xcex8 is a divergence angle of the collimated light emerging from the optical collimator, and La is a distance from the optical collimator to the directivity regulating member.
In order to attain another object described above, the present invention provides a liquid-crystal display apparatus comprising a liquid-crystal display panel; and an illuminating device including light sources, a housing of the light sources that has its inner surfaces covered with a diffuse reflecting layer, an optical collimator for collimating light issued from the light sources and the light reflected by the diffuse reflecting layer, and a directivity regulating member for regulating directivity of the collimated light emerging from the optical collimator.
Preferably, the directivity regulating member has a plurality of optical paths through which the light passes and anti-reflection layers that absorb the light incident on wall surfaces of the optical paths.
Preferably, the following relation is satisfied:
p/tan xcex8xe2x89xa6La
where p is a pitch of emergence of the collimated light from the optical collimator, xcex8 is a divergence angle of the collimated light emerging from the optical collimator, and La is a distance from the optical collimator to the directivity regulating member.
It is also preferable that the liquid-crystal display apparatus further comprises a light diffusing plate for diffusing image-bearing light that has pass ed through the liquid-crystal display panel.
Preferably, the following relation is satisfied:
q/tan xcfx86xe2x89xa6Lb
where q is a pitch of emergence of the collimated light from the illuminating device, xcfx86 is a divergence angle of the collimated light emerging from the illuminating device, and Lb is a distance from the illuminating device to a liquid-crystal layer of the liquid-crystal display panel.